Salt regulation of O-acetylserine(thiol)lyase in Arabidopsis thaliana and increased tolerance in yeast

The cytosolic isoform of O-acetylserine(thiol)lyase (OASTL, EC 4.2.99.8), t he enzyme that catalyses cysteine biosynthesis, is induced in leaves of Ara bidopsis thaliana exposed to salt stress. The protein level increases after 1 d sodium chloride treatment, and progressively for up to 5 d. The overex pression in yeast of the Atcys-3A gene coding for this OASTL isoform can su pport the growth of the yeast cells at high concentrations of sodium chlori de, suggesting that the plant protein is able to confer salt tolerance in y east. Besides, the O-acetylserine(thiol)lyase enzyme activity is not inhibi ted in vitro by cations such as Li+ or Na+. Our results suggest that the pl ant is responding to the salt stress by inducing cysteine biosynthesis as a protection against high ion concentrations. (C) 2001 Editions scientifique s et medicales Elsevier SAS.